In vehicle exhaust systems, it is desirable to provide a pipe joint with high pull-apart strength and with a good fluid seal between the pipes. It is becoming increasingly important to achieve greater reliability and uniformity in providing exhaust pipe couplings with a good fluid seal.
In the Cassel U.S. Pat. No. 4,629,226, granted Dec. 16, 1986, a pipe lap joint is disclosed which provides a collapsible sealing zone in the outer pipe. This is achieved by providing a pair of intersecting end-to-end slots in the outer pipe which provide relief for circumferential contraction of the sealing zone within the overlap region of the pipe ends. A clamping band is disposed around the outside pipe and covers the inboard slot. When the clamping band is tightened around the outside pipe the sealing zone of the outer pipe is collapsed into close fitting engagement with the inner pipe. The intersecting outboard and inboard slots are circumferentially offset with the adjacent sidewalls in substantial alignment with each other and with the inner end wall of the outboard slot in substantial alignment with the outer end wall of the inboard slot. With this alignment and with the sidewalls and end walls of the slots being rectilinear, an inner corner of the outboard slot makes a point-to-point intersection with an outer corner of the inboard slot. With this structure, only a very small amount of collapse of the outer pipe is necessary to cause a sealing engagement between the inner end wall of the outboard slot and the outer end wall of the inboard slot.
The Cassel et al. U.S. Pat. No. 5,588,680 granted Dec. 31, 1996 discloses a pipe lap joint for vehicle exhaust system in which a pair of non-intersecting end-to-end slots are provided to afford relief for circumferential contraction of the sealing zone within the overlap region of the pipe ends. With this construction, precise location of the adjacent corners of the slots is required and the sidewalls and end walls which form the corners are rectilinear. In this pipe joint, a fluid seal is obtained upon tightening of the clamp on the outer pipe even though there is no substantial contraction of the sealing zone by collapse of the slots because a frangible bridging segment of the pipe wall extends between adjacent corners of the slots. Thus, the slots are isolated from each other when the frangible bridging element is either only slightly deformed or when it is completely fractured by collapse of the overlap region of the outer pipe.
In the prior art discussed above reliable and uniform fluid sealing is achieved in such joints. However, the production tooling requires punch and die sets which are subject to relatively short life due to the rectangular or acute angles of the corners of the slots in both the intersecting and non-intersecting slot designs. This results in undesirably high cost in punching the pipe ends to form the slots.
A general object of this invention is to overcome certain disadvantages of the prior art and to provide a pipe lap joint with an improved sealing zone.